1. Field of the Invention
The present invention relates to a printer of the type printing an image on a sheet by pressing the sheet against a print drum with pressing means.
2. Description of the Prior Art
A thermosensitive, digital master making type of stencil printer is known as a simple, convenient printer. A stencil for use with this type of printer has a laminate structure made up of a porous support implemented by Japanese paper fibers, synthetic fibers or a mixture thereof and a thermoplastic resin film (simply film hereinafter) adhered to the support.
The above stencil printer includes a thermal head or similar heating unit including a number of heat generating devices. When the film surface of the stencil is in contact with the thermal head, the thermal head is moved in the main scanning direction in accordance with image data representative of a document image read by a scanner or image data received from a personal computer or a computer, selectively perforating, or cutting, the stencil with the heating devices to thereby make a master. The master thus made is automatically wrapped around the circumference of a cylindrical, porous print drum while being moved in the subscanning direction by a platen roller or similar master conveying means.
Subsequently, ink is fed from ink feeding means arranged inside the print drum to the master while a sheet is fed from a sheet feeding section toward the print drum. The sheet is continuously pressed against the print drum via the master by a press roller, press drum or similar pressing means, so that the ink is transferred to the sheet via the porous portion of the print drum and perforations formed in the master to thereby print an image on the sheet. The sheet thus adhered to the print drum by the adhesion of the ink is peeled off from the print drum by an air knife or blowing/peeling means implemented by a fan and then driven out to a print tray.
The stencil printer of the type described has some problems left unsolved, as will be described hereinafter. If much ink penetrates the master wrapped around the print drum, the amount of ink to be transferred to the sheet increases and brings about an occurrence that the image printed on the sheet runs or that when consecutive printed sheets are stacked, the ink on the underlying sheet is transferred to the reverse surface of the overlying sheet (so-called offset). On the other hand, if the amount of ink penetrated the master is short, then the amount of ink transferred to the sheet is also short, tending to cause the image on the sheet to blur.
Paying attention to the fact that the problems stated above are greatly dependent on the viscosity of the ink and the pressing force of the pressing means, Japanese Patent Laid-Open Publication No. 2004-155170 proposes a stencil printer capable of allowing the pressing force and other various conditions to be set for realizing high image quality.
Generally, a stencil printer includes some mechanisms that produce noise, e.g., contact noise ascribable to hitting of a press roller, which is a specific form of the pressing means, against the print drum, air blow noise and sheet feed noise. Such noise is particularly great when the pressing force of the press roller is increased or when print speed is high. However, the noise particular to printing operation has not been discussed in the past because the stencil printer has, in many cases, been used in an exclusive room.
On the other hand, the current tendency is toward a stencil printer including a controller that operates when the printer is connected to, e.g., a personal computer. Such a modern stencil printer is often situated in an ordinary office instead of an exclusive room, so that noise produced thereby is not negligible.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 2005-154119 and 2004-198889